Okay, let's tackle this question. The question is about Henoch-Schönlein Purpura (HSP), and the options given are a) Palpable purpura, b) Kidneys commonly affected, c) C-ANCA positive, d) Thrombocytopenia. The correct answer is A, right?

First, I need to remember the key features of HSP. HSP is a small vessel vasculitis, typically IgA-mediated. The classic presentation includes a palpable purpura, which is a hallmark. So option a is correct. The purpura is palpable because it's due to inflammation of the blood vessels, causing them to become leaky and form these lesions that can be felt.

Now, option b says kidneys are commonly affected. I know HSP can involve the kidneys, leading to glomerulonephritis, but is it considered "commonly affected"? Maybe in terms of complications, but not all patients have kidney involvement. The primary features are skin, joints, GI, and kidneys. But the question is about what's true. So maybe b is correct, but I need to check if the question is looking for the most characteristic feature.

Option c is C-ANCA positive. C-ANCA is associated with granulomatosis with polyangiitis (GPA), not HSP. HSP is typically negative for ANCA. So c is incorrect.

Option d is thrombocytopenia. HSP is not associated with low platelet counts. In fact, the platelet count is usually normal, and the purpura is due to vasculitis, not platelet issues. So d is wrong.

The correct answer is a) Palpable purpura. The other options have issues. The kidney is a possible complication but not a universal feature. So the most accurate answer here is A.

**Core Concept**
Henoch-Schönlein Purpura (HSP) is an IgA-mediated small vessel vasculitis characterized by **palpable purpura**, arthritis, abdominal pain, and renal involvement. It is distinct from systemic vasculitides like granulomatosis with polyangiitis (GPA), which are ANCA-associated.

**Why the Correct Answer is Right**
**Option A** is correct because **palpable purpura** is the hallmark of HSP. This occurs due to IgA immune complex deposition in dermal vessels, causing inflammation and extravasation of blood into the skin. The lesions are palpable (raised, non-blanching) and typically appear on the lower extremities.

**Why Each Wrong Option is Incorrect**
**Option B:** While renal involvement occurs in 30–50% of HSP cases, it is not a universal feature. The question asks for a "true" statement, not a common complication.
**Option C:** C-ANCA (cytoplasmic anti-neutrophil cytoplasmic antibodies) is specific for GPA, not HSP. HSP is ANCA-negative.
**Option D:** Thrombocytopenia is absent in HSP. The purpura results from vascular injury, not platelet dysfunction or deficiency.

**Clinical Pearl / High-Yield Fact**
**Remember the "4 Ds" of HSP:** **Derm

✓ Correct Answer: D. ab